1. Field of the Invention
The present invention relates to physical vapor deposition methods and articles therefrom, and more particularly relates to ceramic vapor deposition methods and articles made therefrom.
2. Description of the Related Art
In the gas turbine engine art, particularly those developed for use in aircraft, high temperature operating components are exposed to strenuous oxidizing conditions during operation. Typical of such components are the blades, vanes and associated parts disposed in the turbine section of such engines. In order to extend the operating life of such articles, designers have specified coatings for application to article surfaces for oxidation as well as sulfidation protection.
One such coating has been reported as a thermal barrier coating system in a variety of forms. Generally, the thermal barrier coating is a ceramic type coating, examples of which include zirconia generally stabilized with yttria magnesia or calcia. A preferred form of such a system includes a bond coating disposed between the substrate and the ceramic thermal barrier coating. Reported have been bond coatings of the M Cr Al type of alloy in which M is a metal selected from Fe, Ni, Co and their mixtures and alloys. Other elements including Y, rare earths, Pt, Rh, Pd, and Hf, and their combinations have been included in such an M Cr Al alloy to enhance selected properties. Typical U.S. patents describing such a system or elements thereof include U.S. Pat. No. 4,055,705 Stecura, et al issued Oct. 25, 1977; U.S. Pat. No. 4,269,903 Clingman, et al issued May 26, 1981; U.S. Pat. No. 4,321,310 Ulion, et al issued Mar. 23, 1982; U.S. Pat. No. 4,321,311 Strangman issued Mar. 23, 1981; U.S. Pat. No. 4,335,190 Bill, et al issued Jun. 15, 1982; and U.S. Pat. No. 4,880,614 Strangman issued Nov. 14, 1989, all of which are incorporated herein by reference. Other bond coat systems such as aluminides and platinum modified aluminides are suitable. Bruce, et al U.S. Pat. No. 5,418,003 issued May 23, 1995 is incorporated herein by reference, and discloses vapor deposition of ceramic materials involving (a) furnishing an ingot of a ceramic material, (b) treating the ingot to reduce sources of gas within the ingot, and (c) evaporating the ceramic material in the ingot by melting the surface of the ingot with an intense heat source; the evaporated ceramic is then deposited upon a substrate as the ceramic coating. Bruce discloses that the reduced gas content of the ingot decreases the incidence of spitting and eruptions from the molten surface of the ingot, thereby improving the quality of the deposited coating and faciling increases in evaporation rates and coating process production rates. The gas can be trapped in closed pore voids, on surfaces and in cracks in the source material.
While the above coating techniques can provide thermal barrier coatings, these processes, depending upon the materials being used, can suffer from one or more of the following problems (a) raw material impurities, (b) relatively expensive high purity raw materials, (c) relatively slow production rates and/or (d) undesirably high levels of material spitting (eruptions). Low melting point impurities are another source of gas/vapor that causes spitting and eruptions.
Consequently, there is a desire to provide a process (method) for producing thermal barrier coated articles wherein the process allows for the use of cost effective impurity levels, relatively high production rates and relatively low levels of spitting during the deposition process.